This invention relates to an improved method and apparatus for measuring from time to time underground earth/rock shifting conditions so as to monitor for movements therein, by use of measurement means operating in a vertical hole driven into the underground earth/strata. Various techniques for such purposes have been previously set forth in publications known to applicant as follows: U.S. Pat. Nos. 2,292,938; 3,323,216; 3,380,167; 3,381,750; 3,483,745 and 4,044,470; Soiltest Inc., Evanston, Illinois General Catalog Vol. 2, pages 124, 125; and EARTH MANUAL, U. S. Department of Interior Bureau of Reclamation, First Edition--Second Printing, Denver, Colorado 1968 at pages 672-689.
As explained in these prior art references, apparatus for such purposes are conventionally titled "extensometers", and are importantly employed in the science of monitoring earth/rock subsidence/shifting mechanics. The results thereof are applied for example to appropriate design, control and maintenance of mining and tunneling operations; dam abutments; roadway supports; and the like.
This invention obviates important inaccuracies in operation which are inherent in the prior art systems, and furthermore provides for such purposes an overall more versatile apparatus; in that a single and repeatedly usable "torpedo" type suspension device may be lowered into a bore hole for accurately monitoring earth/rock shiftings at any number of desired stations linearly of the bore hole. The system of the invention substantially reduces the number of bore holes which are required to monitor the geologic section; and decreases the time/labor/costs required in securing such readings.